Citations

ABSTRACT Novel β-lactam/β-lactamase inhibitors (βL/βLIs) are important therapies for carbapenem-resistant Pseudomonas aeruginosa (CRPA). However, the global extent of resistance to these agents and the impact of resistance on patient outcomes are unclear. We therefore evaluated patients with CRPA isolates at 35 hospitals (nine countries) from December 2018 to November 2019. Antimicrobial susceptibility testing was performed at a central laboratory by agar dilution for ceftolozane-tazobactam (C/T) and ceftazidime-avibactam (CZA) and by broth microdilution for imipenem-relebactam (I/R). Characteristics and outcomes, including desirability of outcome rankings (DOOR), were compared between patients infected with isolates not susceptible vs susceptible to each agent. Of 800 CRPA isolates, susceptibility to C/T, CZA, and I/R was 69%, 67%, and 33%, respectively. USA isolates ( n = 526) were more frequently susceptible to these agents than isolates from other countries ( n = 274; C/T: 83% vs 42%; CZA: 77% vs 47%; I/R: 37% vs 23%; P < 0.001 for each comparison) and isolates with carbapenemases ( n = 157) were less frequently susceptible than isolates without carbapenemases ( n = 643; C/T: 7% vs 84%; CZA: 24% vs 77%; I/R: 6% vs 39%; P < 0.001 for each comparison). Thirty-day mortality and DOOR were similar overall in patients infected with isolates not susceptible vs susceptible to each βL/βLI. However, the adjusted probability of a better DOOR outcome for a randomly selected patient with bacteremia due to a C/T-not susceptible vs -susceptible isolate was 38.2% (95% confidence interval, 25.6%–52.7%). Resistance to novel βL/βLIs, especially I/R, is common in CRPA, particularly outside the USA and in carbapenemase-producing isolates. Additional treatment options are needed for CRPA infections.

Importance Novel blood culture diagnostics provide rapid antimicrobial susceptibility testing (AST) results for bacteria causing bloodstream infections (BSIs) but have unclear clinical impact. Objective To evaluate clinical outcomes of blood culture testing using a rapid AST method compared with standard AST in patients with BSIs caused by gram-negative bacilli in regions with high prevalence of antimicrobial resistance. Design, Setting, and Participants Open-label randomized clinical trial that enrolled participants from December 2023 to May 2025 (final follow-up, June 18, 2025) at 7 medical centers in Greece (n = 2), India (n = 1), Israel (n = 3), and Spain (n = 1). Hospitalized patients (adults and children) with BSIs caused by gram-negative bacilli were eligible. Statistical analysis was conducted from August 2025 to January 2026. Intervention Patients were randomized to undergo blood culture evaluation using rapid, phenotypic AST directly from positive blood cultures plus standard susceptibility testing (n = 413) vs standard susceptibility testing alone (n = 437). Local antimicrobial stewardship teams reviewed all patients and provided treatment recommendations. Main Outcomes and Measures The primary outcome was a desirability of outcome ranking (DOOR) at day 30, with 3 categories (alive without deleterious events, alive with deleterious events, and death). The difference between rapid and standard testing was summarized as the probability that the DOOR outcomes were more desirable in the rapid testing group. Superiority was concluded if the lower limit of the 95% CI exceeded 50%. Secondary outcomes included 30-day mortality, length of hospitalization, intensive care unit admission, acquisition of hospital-acquired infections, time to effective antibiotic therapy within 3 days, and time to antibiotic escalation or deescalation within 3 days. Results Of the 899 patients randomized, 850 were included in the primary outcome analysis (median [IQR] age, 72 [21] years; 43% female). The probability that DOOR outcomes were more favorable in the rapid testing group was 48.8% (95% CI, 45.3%-52.4%). Median time to effective antibiotic therapy was not different between the groups in the as-randomized population. Median time to antibiotic escalation or deescalation was faster in the rapid testing group by 14 hours (95% CI, 6-22) in the as-randomized population. There were no differences between the groups in other secondary outcomes. In the prespecified subgroup with carbapenem-resistant infections, median time to effective therapy was 9.5 hours in the rapid testing group vs 28 hours in the standard testing group (difference, −18 hours [95% CI, −42 to 6]). Conclusions and Relevance Among patients with gram-negative bacilli BSIs, rapid blood culture AST was not superior to standard testing by DOOR. When considered with other efficacy and safety outcomes, these findings may help inform the use of rapid susceptibility testing in clinical practice. Trial Registration ClinicalTrials.gov Identifier: NCT06174649

ABSTRACT Intrinsic Acinetobacter -derived cephalosporinases (ADCs) in Acinetobacter baumannii are AmpC-type β-lactamases that confer resistance to β-lactam agents, typically through insertion sequence (IS) element-driven overexpression. However, the contribution of ADCs to resistance against advanced β-lactam agents has not been systematically investigated. Given the increasing clinical use of these agents, including cefiderocol, we analyzed the diversity and function of ADC variants in a global collection of carbapenem-resistant A. baumannii (CRAb) isolates. We identified 52 distinct ADC variants in a collection of 428 CRAb clinical isolates from the United States. Among these, variants carrying both a valine substitution at position 292 in the R2 loop and an alanine duplication (ADUP) in the Ω loop consistently conferred stable resistance to cefiderocol. Biochemical and crystallographic analyses demonstrated that ADC-227, which harbors a V292W substitution with an ADUP at position 218a in the Ω loop, exhibits enhanced catalytic efficiencies for ceftazidime and cefiderocol and moderately reduced inhibition by avibactam, leading to resistance not only to cefiderocol but also to ceftazidime–avibactam. Structural studies revealed conformational flexibility of the R2 loop, allowing dynamic accommodation of substrates. Collectively, the findings identify Val292, in combination with an ADUP in the Ω loop, as a mutational “hot spot” for ADCs evolution that may undermine the efficacy of newer β-lactams, including cefiderocol. These results underscore the need for ongoing molecular surveillance of A. baumannii isolates to detect and track the emergence of such variants in clinical settings. IMPORTANCE Carbapenem-resistant Acinetobacter baumannii (CRAb) has been designated as a critical priority pathogen by the World Health Organization (WHO). Cefiderocol has been introduced as a novel therapy against CRAb; however, recent clinical data highlight concerning treatment failures and excess mortality. Understanding resistance mechanisms is therefore essential to preserve the clinical utility of this agent. This study addresses a critical knowledge gap by investigating the role of intrinsic Acinetobacter -derived cephalosporinases (ADCs), which are ubiquitous in A. baumannii and diverse in sequence. By defining specific mutational patterns that endanger cefiderocol activity, this work highlights how chromosomally encoded enzymes can evolve to erode the effectiveness of newer β-lactams such as cefiderocol. These insights underscore the importance of integrating molecular surveillance into clinical practice and antimicrobial stewardship to ensure timely detection of emerging resistance in clinical A. baumannii isolates, ultimately informing treatment strategies and guiding future drug development.

Abstract Background Ceftriaxone-resistant Escherichia coli infections are increasingly common, partially because of the emergence of E. coli sequence type 131 (ST131), including its subclade C2/H30Rx, which produce extended-spectrum β-lactamases. Methods A prospective cohort including 14 US sites, which enrolled monomicrobial ceftriaxone-resistant and susceptible E. coli bloodstream infection (BSI) cases in a 1:1 ratio, was used to compare ST131 versus non-ST131 E. coli BSI, with specific attention to E. coli ST131 C2/H30Rx. Desirability of outcome ranking was determined at 30 days after infection onset. Results This analysis included 282 patients with E. coli BSI; 43% (121/282) were E. coli ST131 and 23% (66/282) belonged to the C2/H30Rx subclade. Resistance to ceftriaxone was present in 79% (96/121) ST131, 86% (57/66) E. coli ST131 C2/H30Rx, and 27% (43/161) E. coli non-ST131. Compared to patients with non-ST131 E. coli BSI, patients with ST131 BSI were older (median 70 years, [Q1 62, Q3 76] years vs 65 years, [51, 74]; P = .005) and more often admitted from long-term care facilities (21/121 [17%] vs 7/161 [4%], P &lt; .001). Overall and empiric carbapenem use was more frequent in the treatment of patients with ST131 BSI compared with non-ST131 BSI (overall 89/121 [74%] vs 50/161 [31%]; empiric: 58/121 [48%] vs 31/161 [19%], P &lt; .001). Desirability of outcome ranking outcomes were similar between groups. Conclusions Most ceftriaxone-resistant E. coli from US patients with E. coli BSI belong to ST131, particularly E. coli ST131 C2/H30Rx, serving as an important driver of carbapenem use.

Abstract Background Carbapenem-resistant Acinetobacter baumannii (CRAb) is a multi-drug resistant, opportunistic pathogen. Colistin is one of a few remaining treatment options, but resistance exists globally. Methods Between 2017 and 2019, 551 CRAb isolates were collected through the international Study Network of Acinetobacter as a Carbapenem-Resistant Pathogen (SNAP). Demographics, clinical characteristics, mortality, and a desirability of outcome ranking (DOOR) measure combining lack of clinical response, unsuccessful discharge, renal failure, and C. difficile infection, were recorded for each patient. A central laboratory measured colistin minimum inhibitory concentrations (MICs), and each isolate was classified as colistin-intermediate (MIC ≤2µg/mL) or resistant (MIC ≥4µg/mL). All isolates were sequenced on the Illumina platform, and the genomes were used to construct a phylogenetic tree and assess for variants within known colistin resistance-related genes. Results 18% of the 551 isolates were colistin-resistant. Compared to patients with colistin-intermediate isolates, patients with resistant strains were more likely to have been admitted from a healthcare facility, but otherwise had similar demographics and Charlson comorbidity indices. Focusing on patients with bloodstream or respiratory infections (n=217) uncovered increased 30-day mortality in patients with monomicrobial, colistin-resistant infections (11/19, p=0.008) when compared to monomicrobial-intermediate (41/102), polymicrobial-resistant (4/20) and polymicrobial-intermediate infections (18/76). Comparative genomics indicated that the majority of isolates belonged to clonal complex 2 (CC2), and that colistin resistance concentrated in certain genetic lineages. Variant analysis uncovered nonsynonymous mutations near and within the histidine kinase domain of pmrB, part of the PmrAB two-component system that regulates lipopolysaccharide modifications which can alter colistin susceptibility. Conclusion In this global cohort, patients with monomicrobial, colistin-resistant CRAb infections had increased mortality. New treatment options are needed for multidrug-resistant CRAb, and this study provides further evidence that pmrB may serve as a worthwhile drug development target. Disclosures Madison Stellfox, MD, PhD, Cumberland Pharmaceuticals: Grant/Research Support Robin Patel, MD, a patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication, a patent on PET imaging of bacterial infection: a patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication, a patent on PET imaging of bacterial infection|MicuRx Pharmaceuticals and bioMérieux: Grant/Research Support|PhAST, Day Zero Diagnostics, DEEPULL DIAGNOSTICS, S.L., Nostics, HealthTrackRx, bioMérieux and CARB-X: Advisor/Consultant|Up-to-Date and the Infectious Diseases Board Review Course: Honoraria David van Duin, MD, PhD, British Society for Antimicrobial Chemotherapy: Editor stipend|Merck: Advisor/Consultant|Merck: Grant/Research Support|Pfizer: Advisor/Consultant|Roche: Advisor/Consultant|Shionogi: Advisor/Consultant Yohei Doi, MD, PHD, GSK: Advisor/Consultant|Meiji Seika Pharma: Advisor/Consultant|Shionogi: Advisor/Consultant|Shionogi: Honoraria

Abstract Background Drug-resistant E. coli is a leading cause of antimicrobial resistance-associated deaths globally. Specifically, resistance to ceftriaxone (CRO-R) is increasing in E. coli. High-risk clonal group ST131 and its pandemic H30 subclone are of high concern yet studies characterizing these infections are limited. We evaluated baseline characteristics and clinical outcomes associated with H30 ST131, non-H30 ST131 and non-ST131 E. coli bloodstream infections (BSI). Methods Patients with monomicrobial carbapenem-susceptible E. coli BSI that were matched 1:1 by study site (CRO-R and CRO-susceptible community-acquired and hospital onset cases) were prospectively enrolled from 14 United States hospitals between November 12, 2020 to April 28, 2021 in the multicenter Study of Highly Resistant E. coli (SHREC). Isolates underwent whole genome sequencing. The primary outcome was a 30-day Desirability of Outcome Ranking (DOOR) after index culture including clinical response to treatment and all-cause mortality. Results There were 92 (33%) H30 ST131, 29 (10%) non-H30 ST131, and 161 (57%) non-ST131 isolates in 282 E. coli BSI (Table 1). Most ceftriaxone resistance was conferred by CTX-M-15 produced by H30 ST131 isolates (Figure 1, Table 1). H30 ST131 BSI patients were older (median age [IQR] 70.5 [63,76] vs. 67 [56,77] vs 65 [51,74] years, p = 0.017), had higher Charlson comorbidity indices (3 [2,5] vs. 2 [1,4] vs. 2 [1,4], p=0.009), and were more often admitted from long-term care facilities (18/92 [20%] vs. 3/29 [10%] vs. 7/161 [4%], p = 0.003) compared to non-H30 ST131 and non-ST131 BSI patients. Among H30 ST131 isolates, high rates of antibiotic resistance were observed to cephalosporins and fluoroquinolones, resulting in significantly more carbapenem use compared with non-H30 ST131 and non-ST131 isolates (75/92 [82%] vs. 14/29 [48%] vs. 50/161 [31%], p &lt; 0.001) (Figure 2). 30-day DOOR and hospital length of stay did not differ between groups (Table 2). Conclusion Compared with non-H30 ST131 and non-ST131 E. coli BSI, H30 ST131 E. coli BSI have a unique epidemiology with more healthcare exposures, comorbidities and antibiotic resistance and are more likely to be treated with carbapenems, though no significant difference in clinical outcomes was observed. Disclosures Yohei Doi, MD, PHD, AbbVie: Honoraria|Entasis: Grant/Research Support|Gilead: Advisor/Consultant|GSK: Advisor/Consultant|Meiji Seika: Advisor/Consultant|Moderna: Advisor/Consultant|Pfizer: Advisor/Consultant|Shionogi: Advisor/Consultant|Shionogi: Honoraria Elie Saade, MD, MPH, FIDSA, Janssen Global Services: Advisor/Consultant|Janssen Global Services: Advisor/Consultant|Janssen Research and Development: Advisor/Consultant|Janssen Research and Development: Advisor/Consultant Loren G. Miller, MD MPH, Armata: Grant/Research Support|Contrafect: Grant/Research Support|GSK: Grant/Research Support|Merck: Grant/Research Support|Paratek: Grant/Research Support Michael J. Satlin, MD, AbbVie: DSMB participant|bioMerieux: Grant/Research Support|Merck: Grant/Research Support|Selux Diagnostics: Grant/Research Support|SNIPRBiome: Grant/Research Support W. Charles Huskins, MD, MSc, ADMA Biologics: Advisor/Consultant|Bristol Myers Squibb: Stocks/Bonds (Public Company)|Pfizer: Advisor/Consultant|Pfizer: Stocks/Bonds (Public Company)|Zimmer Biomet: Stocks/Bonds (Public Company) Carol Hill, PhD, Glaxo SmithKline: Retirement Health, Cash Balance Plan|Glaxo SmithKline: Stocks/Bonds (Public Company) Robin Patel, MD, a patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication with royalties paid by Samsung to Mayo Clinic, a: See above|MicuRx Pharmaceuticals and BIOFIRE: Grant/Research Support|PhAST, Day Zero Diagnostics, Abbott Laboratories, Sysmex, DEEPULL DIAGNOSTICS, S.L., Netflix, Oxford Nanopore Technologies and CARB-X: Advisor/Consultant|Up-to-Date and the Infectious Diseases Board Review Course.: Honoraria Vance G. Fowler, MD, MHS, Affinergy: Advisor/Consultant|ArcBio: Stocks/Bonds (Private Company)|Armata: Advisor/Consultant|Astra Zeneca: Advisor/Consultant|Astra Zeneca: Grant/Research Support|Basilea: Advisor/Consultant|Basilea: Grant/Research Support|ContraFect: Advisor/Consultant|ContraFect: Grant/Research Support|Debiopharm: Advisor/Consultant|Destiny: Advisor/Consultant|EDE: Grant/Research Support|Genentech: Advisor/Consultant|Genentech: Grant/Research Support|GSK: Advisor/Consultant|Janssen: Advisor/Consultant|Karius: Grant/Research Support|MedImmune: Grant/Research Support|Merck: Grant/Research Support|sepsis diagnostics: Patent pending|UptoDate: Royalties|Valanbuio: Stocks/Bonds (Private Company)|Valanbuio: Stocks/Bonds (Private Company) David van Duin, MD, PhD, Merck: Advisor/Consultant|Merck: Grant/Research Support|Pfizer: Advisor/Consultant|Qpex: Advisor/Consultant|Roche: Advisor/Consultant|Shionogi: Advisor/Consultant|Shionogi: Grant/Research Support

ABSTRACT Ledaborbactam (formerly VNRX-5236), a bicyclic boronate β-lactamase inhibitor with activity against class A, C, and D β-lactamases, is under development as an orally bioavailable etzadroxil prodrug (VNRX-7145) in combination with ceftibuten for the treatment of urinary tract infections. At ceftibuten breakpoints of ≤1 mg/L (EUCAST) and ≤8 mg/L (CLSI), 92.5% and 99.0%, respectively, of 200 carbapenem-resistant Klebsiella pneumoniae isolates, predominantly K. pneumoniae carbapenemase producing, were susceptible to ceftibuten-ledaborbactam (ledaborbactam tested at a fixed concentration of 4 mg/L) compared to 4.5% and 30.5%, respectively, to ceftibuten alone.

Abstract Background The CDC reported a 35% increase in hospital-onset (HO) carbapenem-resistant Enterobacterales (CRE) infections during the COVID-19 pandemic. We evaluated patient outcomes following HO and community-onset (CO) CRE bloodstream infections (BSI). Methods Patients prospectively enrolled in CRACKLE-2 from 56 hospitals in 10 countries between 30 April 2016 and 30 November 2019 with a CRE BSI were eligible. Infections were defined as CO or HO by CDC guidelines, and clinical characteristics and outcomes were compared. The primary outcome was desirability of outcome ranking (DOOR) 30 days after index culture. Difference in 30-day mortality was calculated with 95% CI. Results Among 891 patients with CRE BSI, 65% were HO (582/891). Compared to those with CO CRE, patients with HO CRE were younger [median 60 (Q1 42, Q3 70) years versus 65 (52, 74); P &lt; 0.001], had fewer comorbidities [median Charlson comorbidity index 2 (1, 4) versus 3 (1, 5); P = 0.002] and were more acutely ill (Pitt bacteraemia score ≥4: 47% versus 32%; P &lt; 0.001). The probability of a better DOOR outcome in a randomly selected patient with CO BSI compared to a patient with HO BSI was 60.6% (95% CI: 56.8%–64.3%). Mortality at 30-days was 12% higher in HO BSI (192/582; 33%) than CO BSI [66/309 (21%); P &lt; 0.001]. Conclusion We found a disproportionately greater impact on patient outcomes with HO compared to CO CRE BSIs; thus, the recently reported increases in HO CRE infections by CDC requires rigorous surveillance and infection prevention methods to prevent added mortality.

ABSTRACT Taniborbactam, a bicyclic boronate β-lactamase inhibitor with activity against Klebsiella pneumoniae carbapenemase (KPC), Verona integron–encoded metallo-β-lactamase (VIM), New Delhi metallo-β-lactamase (NDM), extended-spectrum beta-lactamases (ESBLs), OXA-48, and AmpC β-lactamases, is under clinical development in combination with cefepime. Susceptibility of 200 previously characterized carbapenem-resistant K. pneumoniae and 197 multidrug-resistant (MDR) Pseudomonas aeruginosa to cefepime-taniborbactam and comparators was determined by broth microdilution. For K. pneumoniae (192 KPC; 7 OXA-48-related), MIC 90 values of β-lactam components for cefepime-taniborbactam, ceftazidime-avibactam, and meropenem-vaborbactam were 2, 2, and 1 mg/L, respectively. For cefepime-taniborbactam, 100% and 99.5% of isolates of K. pneumoniae were inhibited at ≤16 mg/L and ≤8 mg/L, respectively, while 98.0% and 95.5% of isolates were susceptible to ceftazidime-avibactam and meropenem-vaborbactam, respectively. For P. aeruginosa , MIC 90 values of β-lactam components of cefepime-taniborbactam, ceftazidime-avibactam, ceftolozane-tazobactam, and meropenem-vaborbactam were 16, >8, >8, and >4 mg/L, respectively. Of 89 carbapenem-susceptible isolates, 100% were susceptible to ceftolozane-tazobactam, ceftazidime-avibactam, and cefepime-taniborbactam at ≤8 mg/L. Of 73 carbapenem-intermediate/resistant P. aeruginosa isolates without carbapenemases, 87.7% were susceptible to ceftolozane-tazobactam, 79.5% to ceftazidime-avibactam, and 95.9% and 83.6% to cefepime-taniborbactam at ≤16 mg/L and ≤8 mg/L, respectively. Cefepime-taniborbactam at ≤16 mg/L and ≤8 mg/L, respectively, was active against 73.3% and 46.7% of 15 VIM- and 60.0% and 35.0% of 20 KPC-producing P. aeruginosa isolates. Of all 108 carbapenem-intermediate/resistant P. aeruginosa isolates, cefepime-taniborbactam was active against 86.1% and 69.4% at ≤16 mg/L and ≤8 mg/L, respectively, compared to 59.3% for ceftolozane-tazobactam and 63.0% for ceftazidime-avibactam. Cefepime-taniborbactam had in vitro activity comparable to ceftazidime-avibactam and greater than meropenem-vaborbactam against carbapenem-resistant K. pneumoniae and carbapenem-intermediate/resistant MDR P. aeruginosa .

Abstract Background Use of anti-carbapenem-resistant Enterobacterales (anti-CRE) agents such as ceftazidime/avibactam has been associated with improved clinical outcome in cohorts that primarily include patients infected with CRE that are resistant to meropenem (MCRE). Objectives To clarify whether patients with CRE resistant to ertapenem but susceptible to meropenem (ertapenem-only-resistant Enterobacterales; EORE) benefit from therapy with anti-CRE agents. Methods Patients treated for CRE infection in hospitals in the USA between 2016 and 2019 and enrolled in the CRACKLE-2 study were included. The primary outcome was the desirability of outcome ranking (DOOR) assessed at 30 days after index cultures. Results The EORE group included 213 patients and the MCRE group included 643. The demographics were similar between the groups except for the patients’ race and origin before admission. The MCRE group received anti-CRE agents for definitive therapy significantly more frequently compared with the EORE group (30% versus 5% for ceftazidime/avibactam). We did not observe a significant difference between the groups in the adjusted DOOR probability of a more desirable outcome for a randomly selected patient in the EORE group compared with the MCRE group (52.5%; 95% CI, 48.3%–56.7%). The MCRE group had a similar proportion of patients who died at 30 days (26% versus 21%) and who were discharged to home (29% versus 40%), compared with the EORE group. Conclusions Patients with clinical EORE infection rarely received anti-CRE agents, but attained similar outcomes compared with patients with MCRE infection. The findings support current IDSA treatment guidance for meropenem- or imipenem-based therapy for treatment of EORE infections.